1. Field of the Invention
The present invention relates to a power management device, and more particularly, to a power management device of an electronic card.
2. Description of the Related Art
With the advance of electronic technology, the electronic devices are getting smaller, for example, notebook computers, pocket PCs, or personal digital assistants (PDAs). These small type electronic devices are portable and powerful in calculation so as to provide a great convenience to users. However, since they are compact, they are generally provided with basic circuitry, and other circuit modules, such as memory cards, modems, local area network cards, etc., are typically implemented as external electronic cards to perform the corresponding functions. In general, this electronic card has at least one functional module and an interface, such as the PCMCIA/CF interface for being inserted into the electronic device.
Conventionally, the above functional module of the electronic card is powered to operate by the power source of the interface. However, the power source on the interface is limited and thus, if the functional module is a power-consuming module, such as the GPRS module, wireless network module, or GPS module, the electronic card may not be operated due to power insufficiency. For example, the maximum current supplied by a CF interface is 75 mA under 3V and 25 degrees and 100 mA under 5V and 25 degrees, but the driving current required by GPRS (global package radio service) is as high as 300 mA.
One direct approach to resolve above problem is to add a battery to the electronic card so as to supply sufficient power to the functional module of the electronic card. Under such an architecture, it is important to properly manage the power source provided by the interface and the power of the battery for ensuring the proper operation of the functional module.